Electric cables for transformer leads and the like



March 18, 1958 1 0, u \1 2,827,510

ELECTRIC CABLES FOR TRANSFORMER LEADS AND THE LIKE Filed Aug. 27, 1955IN VEN TOR. M W m BY m& 91

United States Patent ELECTRIC CABLES FOR TRANSFORMER LEADS AND THE LIKEGeorge 0. Hunsinger, Arnbridge, Pa., assignor to National ElectricProducts Corporation, Pittsburgh, Pa., a corporation of DelawareApplication August 27, 1953, Serial No. 376,958

11 Claims. (Cl. 174-122) This invention relates to conductors havinguntreated, crumpled paper insulation. The invention is primarilyconcerned with transformer leads which are placed in oil when in use.The primary purpose of the crumpled paper is to provide insulation of amaximum radius, and to leave a substantial volume of voids into whichthe oil enters to supply the dielectric strength for the insulation.

Flexibility of the insulation is an important advantage because sometransformer leads require bends of fairly short radius; and with paperinsulation sharp bends which break the insulation leave the outsidecurve of the conductor with an insulation covering of less radialthickness than intended. The danger of such breakage of the insulationis increased when conductors have greater radial thickness of insulationbecause there is increased distortion of the insulation at greaterdistances from the neutral axis of the bend.

It is an object of the invention to provide an improved, paperinsulation of greater flexibility than paper insulation of the priorart. Another object of the invention is to obtain a maximum radialthickness of insulation with more voids for the admission of oil intothe insulation.

The insulation of this invention can be wound in a single pass or inmultiple passes through spinning heads of a machine for applying theinsulation to the wire conductor. It can be applied with the same ordifferent angles of lay. For greater flexibility the different layers ofinsulation may be wound with the same angle of lay. This requires thatthe spinning head, which applies outer layers of insulation, runsomewhat more slowly than those which apply the inner layers. In orderto compensate for the greater radius of the outer layer of paperinsulation, when using the same angle of lay, this invention suppliesmore paper to the outer layer; and in the preferred construction, theadditional paper is obtained by crumpling more strands into the sameunit length of conductor. This permits the use of strands of the samewidth for all of the reels of the spinning heads.

Other objects, features, and advantages of the invention will appear orbe pointed out as the description proceeds.

In the drawing, forming a part hereof, in which like referencecharacters indicate corresponding parts in all the views:

Fig. 1 is a fragmentary, ectional view of a transformer showing the wayin which the transformer leads of this invention are connected betweenthe core and terminals of a transformer;

Fig. 2 is a diagrammatic view showing the relative advances of a helicalwrapping for inner layers of small radius;

Fig. 3 shows the different pitch of the insulation when the same angleof lay is used for outer layers of larger radius than in Fig. 2;

Fig. 4 is a diagrammatic view showing the way in which multiple strandsof untreated paper are transversely crumpled and wrapped around aconductor and around inner layers while passing through a spinning head;

Fig. 5 is a greatly enlarged, transverse sectional view taken on theline 55 of Fig. 4; and

Fig. 6 is a reduced scale, diagrammatic view showing the relation of thepaper dies to the conductor when looking along the axis of theconductor.

Fig. 1 shows a transformer core 10 enclosed in a housing 11 which isfilled with oil 12. The housing has a cover 14 and terminals surroundedby insulators 15 and 16 attached to the cover. Only two such terminalsare shown, but it will be understood that there are usually others atspaced regions across the transformer housing.

Power lines 18 extend from the insulators 15 and 16. Within thetransformer the power lines are connected to the windings of the core 10by transformer leads 2%.

Figs. 2 and 3 are diagrammatic views showing the way in which a strandof crumpled paper is wrapped on cables of different diameter in a helixthat has the same angle of lay for the layer of large radius as for thelayer of small radius.

in Figure 2 a crumpled paper strand 26 is Wrapped directly on a strandedmetal conductor 28. The strand of paper insulation 26 is supplied to theconductor 28 at an acute angle to the conductor so as to wrap in a helixabout the conductor. This angle of the helix, or angle of lay, isdesignated by the reference character 30. Each convolution of the strand26 has a Width W and overlaps the preceding convolution by a distance 0.In the actual construction of the first layer of insulation, fourstrands of paper insulation 26 are used in the first layer of insulationin order to obtain more overlapping and a greater radial thickness forthis first layer of insulation, but the single strand shown in Fig. 2illustrates the principle.

Fig. 3 shows a crumpled paper strand 26, having the width W, applied tothe cable 29 as part of one of the outer layers of insulation. the cablein Fig. 3 with the same helical angle, or angle of lay 30, as in Fig. 2;but because of the increased radius of the cable 29 there is nooverlapping of the successive convolutions of the strand 26.

With this invention, the desired overlapping of the convolutions ofsuccessive strands of insulation is obtained by using more strands for alayer of insulation which has larger radius. By using eight strands ofcrumpled paper 25 instead of the single strand shown in Fig. 3, thisinvention obtains the desired overlapping of successive strands and alsoobtains a substantial radial thickness for this layer of insulation withincreased radius.

Although the preferred embodiment wraps successive layers of insulation,in opposite directions, that is, with alternate right and left-handhelixes, the flexibility of the insulation is improved by having theangle of lay, particularly of those layers which wrap in the samedirection, equal for all layers.

Fig. 4 is a diagrammatic view illustrating the construction of the cable29 with plural strands of crumpled paper in each layer of insulation,and more paper in the outer layer. This figure does not illustrate theway in which the strands are actually applied to the cable since adescription of the operation of the apparatus for applying the crumpledpaper is not necessary for a complete understanding of this invention.

The application of crumpled paper for insulation is known and foracomplete understanding of this invento prevent removal of the crumpledeffect.

The strand 26 is applied to' a first layer 34 of crumpled paperinsulation made up of four strips 36 which are crumpled into strands 2by constricted dies designated generally by the reference character 38.

The paper strips 36 are preferably untreated kraft paper. This firstlayer of insulation is applied directly over the bare metal conductor 28with a right-hand lay in the illustrated construction. A similar layer42 of crumpled paper insulation, made up of four strands 26, is appliedover the first layer 34 with a left-hand lay. The second layer 42 isalso made up of crumpled, untreated kraft paper which is drawn throughmulti-dies, usually separate dies for the separate strips 36. Thereference character 38 designates representative diagrammatic die meansfor crumpling the paper.

, An outer layer 44, of crumpled paper insulation, which is alsopreferably made of untreated kraft paper, is applied over theintermediate layer 42. In order to obtain comparable overlap of thecrumpled paper strands in spite of the greater radius of the upper layer44, with the same helix angle as the other layers, more paper is used tomake this layer.

This additional paper can be obtained by using strips 36 which are widerthan those used for the other layers, but in the constructionillustrated, strips of the same width are used with an increase in thenumber of the strips. Figure 4 shows die means 46 for crumpling andoverlapping four paper strips 36; and shows other die means 48 forcrumpling and overlapping an additional four strips 36 which areoverlapped as a group with the other strips which are crumpled by thedie means 46.

The layer 44 is applied with a right-hand lay at the same helix angle asthe strands 26 of the first layer. Outside of the outer layer 44 ofcrumpled paper insulation, there is a braid 50 made of loosely wovencloth. This braid 50 provides some mechanical protection for thecrumpled paper layer 44, but there is ample space between the threads ofthe braid 50 to permit oil to pass through the braid and into the voidsof the crumpled paper insulation.

The construction illustrated is economical to manufacture and has highlysatisfactory insulating qualities for use in transformer leads, andother purposes where the cable is not subject to substantial mechanicalabrasion.

Figure 6 is another diagram to show the application of the insulation inlayers; and the same illustrative expedient for showing the die means isused as in Figure 4.

Some changes and additions in the illustrated embodiment can be madewithout departing from the invention as defined in the claims.

What is claimed is:

1. An insulated electrical cable including a metal conductor, a wrappingof untreated, crumpled paper applied directly to the surface of theconductor as the first layer of insulation, other layers of insulationoutside of said first layer and each consisting of untreated, crumpledpaper, each of the layers of insulation comprising a plurality ofhaphazardly crumpled paper strips crumpled in directions substantiallynormal to the longitudinal edges of the strips and helically wound, theouter layer of crumpled paper including more strips of paper than theinner layers.

2. An insulated electrical cable comprising a central metal conductorwith multiple layers of crumpled paper insulation surrounding it, theinner layer of insulation bearing directly against the metal conductorand con sisting of untreated crumpled paper, and a plurality ofsuperimposed layers of insulation comprising similar untreated crumpledpaper, each layer of insulation comprising multiple strands of thecrumpled paper wrapped as helixes around the conductor, each strandincluding a haphazardly crumpled paper strip crumpled in directionssubstantially normal to the longitudinal edges of the strip, the outerlayer of insulation having more strands of the crumpled paper than theinner layers.

3. A flexible electrical cable for transformer leads that are to beimmersed in oil when in service, said cable comprising a stranded metalconductor, a plurality of layers of crumpled paper insulationsurrounding said conductor including a first layer of crumpled papermade of a number of individual strips of paper crumpled and contiguousto one another and forming with one another a wrapping strand wound in ahelix in direct contact with the surface of the conductor and with someoverlapping of the rearward edge of each convolution and the forwardedge of the next convolution, a second layer of crumpled paper made of anumber of individual and contiguous strips wrapped over the first layerin a manner similar to the wrapping of the first layer on the conductorbut with an opposite direction of lead of the helix, and a third layerof crumpled paper insulation made of a greater number of individualstrips than the first layer, the strips having the same direction oflead and substantially the same helix angle as the strips of the firstlayer of insulation but the greater number of strips of the third layerforming a wider wrapping strand to compensate the greater radius of thethird layer Without change in the helix angle, the additional strips ofthe third layer adding substantial additional width and each wrappingstrand of the third layer having some overlapping of the rearward edgeof each convolution and the forward edge of the next convolution, and aporous braided cloth cover over the outside layer of crumpled paper foradmitting oil freely into the open spaces pro vided by the crumpling ofthe paper.

4. A transformer lead including a central metal con ductor, a layer ofinsulation comprising a plurality of haphazardly crumpled paper stripscrumpled in directions substantially normal to the longitudinal edges ofthe strips and applied directly to the surface of the metal conductor asthe first layer of insulation, a plurality of other layers of insulationover the first layer and each comprising similarly crumpled paper stripswrapped as helixes around the conductor with the helixes of thesuccessive layers of insulation being Wound to the right and left,respectively and with all layers of insulation, except the extreme outerlayer comprising untreated crumpled paper, a braided cloth covercomprising the extreme outer layer of insulation with loosely woven meshfor admitting oil freely to the voids by the crumpled paper, the outerlayer of paper insulation including more strips of paper than the otherlayers.

5. An insulated conductor comprising a central metal conductor, a firstlayer of insulation applied directly to the surface of the metalconductor and consisting of a plurality of strands of helically-Wound,transversely crumpled, untreated paper, each strand including ahaphazardly crumpled paper strip crumpled in directions substantiallynormal to the longitudinal edges of the strip, a plurality of outerlayers of insulation consisting of other strands of similarly crumpled,untreated paper, successive layers of the insulation having the strandswrapped as right and left hand helixes, respectively, and the outerlayer of crumpled paper insulation having strands of the same originalwidth as the inner layers but with more strands for each unit length ofthe conductor to compensate for the greater radius of the outer layer ofcrumpled paper insulation.

6. An insulated electrical cable including a metal con ductor wire, afirst layer of insulation applied directly to the metal conductor wireand consisting of strands of haphazardly crumpled paper strips crumpledin directions substantially normal to the longitudinal edges of thestrips, other layers of similar insulation outside of the first layer,the subsequent layers of insulation being also made of strands ofsimilarly crumpled paper strips, the lay of the strands of thesuccessive layers being of the same angle, but the outer layer ofcrumpled paper insulation containing more paper per unit length ofc0nductor than the inner layers to compensate for the greater radiuswith the same angle of lay of the strands.

7. An insulated elcertical cable comprising a central wire, a firstlayer of insulation applied directly to the surface of the wire andconsisting of untreated strands of haphazardly crumpled paper stripscrumpled in directions substantially normal to the longitudinal edges ofthe strips, a plurality of other layers outside of the first layer, saidother layers consisting of similar strands of untreated, crumpled paper,each of the layers of insuiation having its strands helically wound withsubstautially the same helix angle and with successive layers havingright and left hand leads, respectively, the outer layer of crumpledpaper insulation consisting of substantially twice as many strands ofpaper to compensate for the greater radius with the same helical anglefor the strands, and a braided cover overlying the outer layer ofcrumpled paper insulation.

8. An electrical cable comprising a central metal conductor, a number oflayers of insulation applied to the surface of the wire and consistingof untreated strands of haphazardly crumpled paper strips crumpled indirections substantially normal to the longitudinal edges of the strips,successive layers having the same number of strands of paper and with adiflerent angle of pitch and the successive layers having the samedirection of lead, and a braided or woven cover overlying the outerlayer of crumpled paper insulation.

9. An electrical cable comprising a central metal conductor, a number oflayers of insulation applied to the surface of the wire and consistingof untreated strands of haphazardly crumpled paper strips crumpled indirections substantially normal to the longitudinal edges of the strips,successive layers being applied with the same number of strands of paperand with a different angle of pitch and with successive layers appliedwith alternate layers having left and right hand lead, and a braided orWoven cover overlying the outer layer of crumpled paper insulation.

10. An electrical cable comprising a central metal conductor, a numberof layers of insulation applied to the surface of the wire, andconsisting of untreated strands of haphazardly crumpled paper stripscrumpled in directions substantially normal to the longitudinal edges ofthe strips, each layer being applied with a diiferent angle of pitch andwith the successive layers applied with the same directions of lead, theouter layers comprising more strands of paper than the inner layers, anda braided or woven cover overlying the outer layer of crumpled paperinsulation.

11. An electrical cable comprising a central metal conductor, a numberof layers of insulation applied to the surface of the Wire andconsisting of untreated strands of haphazardly crumpled paper stripscrumpled in directions substantially normal to the longitudinal edges ofthe rips, the successive inner layers being applied with the same numberof strands of paper and with a ditferent angle of pitch and withsuccessive layers applied with alternate layers having left and righthand lead, the outer layer comprising more strands of paper than theinner layers, and a braided or woven cover overlying the outer layer ofcrumpled paper insulation.

References Cited in the file of this patent UNITED STATES PATENTS2,015,714 Del Mar Oct. 1, 1935 2,281,111 Robinson et al. Apr. 28, 19422,607,822 Crandall Aug. 19, 1952 2,607,823 Camilli et al Aug. 19, 19522,607,824 Camilli et a1. Aug. 19, 1952

